Upon completion of drilling a well, cement slurries are pumped down the hole, and placed in the annulus between a casing pipe and subterranean formation, or between two casing strings. The cement slurry upon setting can isolate the cemented formation zones and can prevent fluid communication (often referred to as zonal isolation) between the cemented zones, or between the formation and the wellbore annulus. However, the cement sheath, during the production phase of the well, is subjected to a variety of stresses from the wellbore side, such as cyclic pressure and temperature changes, fluid density changes, stimulation operations such as perforations, fracturing, acidizing and remedial operations. As a result, the cement may develop cracks and fractures which can provide conductive pathways or channels, through which formation fluids can flow into, accumulate, and build pressure at the well head. Because of the hazards posed by such situations, wells may need to be shut down until successful remedial operations such as squeeze cementing, or settable resin injection are carried out. The success of such remedial operations is not always assured or predictable.
Current approaches to develop cement compositions which are, primarily, resistant to cyclic stresses and sudden impact events during the life of the well, and secondarily to self-heal in case of cracking under stress are complex or only mildly effective. For example, some approaches to improve cyclic stress resistance of cement compositions include using foamed cement slurries, which require highly specialized equipment such as cryogenic equipment to supply nitrogen. Other approaches such as inclusion of particulate elastomers, while representing a simpler solution, suffer from problems such as poor adhesion between cement and liquid elastomer, phase separation in the slurry, or difficulties in obtaining in suitable particle sizes.